22 World Heolth • 51 st Year, No. 4, July-August 1998
Zoonoses and the immune system
Ashley Robinson
The benefits of pet ownership can outweigh the risks of infection, provided that common-sense pet care guidelines are followed.
M
any people today have a weakened immune system as a result of chronic infec- tion or because they have received powerful drugs during cancer treat- ment or have undergone organ transplants. The problem is set to become more acute in the future as the proportion of elderly people, who are more likely to develop cancer than young people, continues to grow. Naturally, anyone suffering from a disorder of the immune system must take care to avoid unnecessary exposure to disease, but to what lengths should they go?Should they, as some have sug- gested, part with their pets or change their job if it involves potential contacts with zoonotic agents?
Pets and the sick: a dilemma
"People come to visit but they can only stay an hour or so and then they have to leave. My cat, she's always there". These words from an HIV- infected person point to a dilemma faced all too often by people whose immune system may be failing to make the normal response to the many infectious agents encountered in daily activities.
Well-meaning friends, health care providers and even physicans may advise those infected with HIV or suffering from other immune disorders to get rid of their pets
The risk of catching o disease from a pet is considerably reduced if animals are checked by a veterinarian and ii certain rules of animal hygiene are respected.
Photo WHO/PAHO/C Gaggero
because they are potentially a source of disease. However, recent studies in the USA have shown that there is little difference in the levels of pet ownership between the HIV-infected and the rest of the population. This suggests that, to a large extent, the advice is being ignored, probably because for many the unconditional affection and companionship offered by pets are hard to do without.
When people fall sick, or are unable to work, when even their best friends may desert them, the psychological benefits of pet ownership may often outweigh the risks of acquiring a zoonotic infection. In view of the dilemmas that can arise, it is impor- tant to know what the real dangers are and what steps can be taken to minimize them.
The major zoonoses that HIV- infected and other immunodeficient persons acquire are:
(a) Enteric (intestinal) infections that may result in life-threatening diarrhoea such as salmonellosis, campylobacteriosis, and cryp- tosporidiosis. These infections are most likely to be either water- borne or acquired indirectly through food. On occasion, however, they are acquired directly from animals, especially if these have diarrhoea.
(b) Systemic infections which in- volve the body as a whole.
Toxoplasmosis, tuberculosis, cryptococcosis, Q fever and cat scratch fever are all examples of this type of infection which may lead to encephalitis (inflamma-
World Health • SlstYear, No. 4, July-August 1998 23
Pet selection and animal handling guidelines for the immunosuppressed
l . Before purchasing a new animal, contact a veterinarian for information and help. It is best to avoid stray animals as well as puppies, kittens, reptiles and monkeys; these are more likely to carry infections. Neutered animals (castrated or spayed) are safer as they are less likely to roam.
2. Domestic animals have their own immunodeficiency viruses such as the feline leukaemia virus. As a result, infected animals can be at greater risk than others of acquiring zoonotic infections Cats, for example, should be tested and, if negative, vaccinated before adoption or purchase. Animals can also be tested for zoonotic infections before purchase, but a negative test is no guarantee that a subsequent infection will not occur. Measures to avoid infections are likely to be more effective in the long run.
3. After purchase, keep the animal healthy and clean, as sick animals are more likely to spread infection via faeces, urine or saliva. Consult a veterinarian for diagnosis and treatment, as well as ensuring that the appropriate vaccinations ore given.
4. Feed pet animals and birds the pet foods available in shops, or cooked foods Do not feed them raw or undercooked meat
or eggs, or unpasteurized milk, and do not let animals drink from a toilet.
5. As a general rule keep animals indoors; when outside, keep them on a leash or tether.
6. Keep animals free of parasites, including fleas and ticks, and keep their sleeping and feeding areas clean.
7. Keep claws short to avoid scratching. In extreme cases the claws can be removed entirely. Animal-inflicted iniuries should always receive immediate first aid, and a doctor should be consulted.
8. Always wash hands thoroughly after handling animals and weor disposable gloves when cleaning up faeces or vomit or when disposing of litter. The agent Toxoplosmo gondii takes about 48 hours to become infectious in cot faeces, so litter should be removed daily Similar precautions should be taken when working with livestock, and care should be exercised when dealing with animals which have diarrhoea (particularly when they are young) or when handling animals that have recently been aborted.
tion of the brain) and/or pneumo- nia. Most of these agents can cause illness in animals, but the infected animal may appear to be quite healthy. Zoonotic diseases are most likely to be found in younger animals, animals under stress or living in crowded condi- tions such as kennels, and out- door animals which hunt for part of their diet.
before drinbng it. Thjs can be done by boiling it. Finally, it is worth remembering that the human strain of tuberculosis is easily transmitted to dogs. Therefore if a dog is diag- nosed as having this disease there may be a human source of infection in the immediate environment.
A helping hand
In some places, local organizations have been formed to provide infor- mation and assistance to HIV- infected pet owners. Volunteers can be of enormous help: they can change litter boxes, clean fish tanks and bird cages, walk dogs, assist with flea control in the home, take care of pets when the owners are hospitalized and, if necessary, arrange for their adoption.
Tuberculosis and HIV
There are several different types of tuberculosis that affect humans, and tuberculosis is a relatively common illness in HIV-infected people.
Although birds are occasionally infected with the avian type, humans usually acquire this strain from their immediate environment rather than from an avian source. A marine type of tuberculosis has occasionally been transmjtted to people with HIV infection, usually from a contami- nated aquarium. The bovine tuber- culosis type is no longer a major cause of infection in industrialized countries. The situation in develop- ing countries is more problematic;
where the prevalence of both HIV and tuberculosis is high, there is a real risk that people could be in- fected with tuberculosis from their cattle. Where systematic pasteuriza- tion is not practised, it is therefore very important to sterilize milk
A moment of tenderness is shared by this man and his pet. The association PAWS {Pets are Wonderful Support), based in California, USA, provides volunteers who take care of all aspects of pets' hygiene for people with HIV/AIDS The emotional support provided by pets far outweighs the risk of disease.
Photo WHO/PAWS/P Baucher
In conclusion, pets can be good for our health and emotional well- being. For those with immune disorders, the benefits of having pets can be especially important.
Providing that common-sense guide- lines are followed there are no sig- nificant reasons why these benefits should be denied. •
Dr Ashley Robinson is Professor and Clinical Epidemiologist, Middle East Regional Cooperation Proiect, Tufts University/School of Veterinary Medicine, 200 Westboro Road N, Grafton, MA O 1536, USA.
The September-October issue of World Health will report (on page 28) on the 8th lntemational Conference on Human-Animal Interaction on "The changing roles of animals in society"
(Prague, September 1998).
